Michal Douša - Profile on Academia.edu (original) (raw)
Papers by Michal Douša
Separation of pharmaceutically active compounds by multimodal chromatography with ultraviolet detection
Separation science plus, Jun 18, 2021
This research focused on pharmaceutically active ingredients analyzed by mixed‐mode liquid chroma... more This research focused on pharmaceutically active ingredients analyzed by mixed‐mode liquid chromatography. For this purpose, 16 analytes were chosen with acidic, basic, or neutral properties that were analyzed under different conditions. These analytes play an important role in the pharmaceutical industry and improved separation will make drug control more efficient. Mixed‐mode chromatography is becoming an increasingly popular method for the analysis of diverse compounds due to the process being based on the combination of two or more interaction modes. The use of the mixed‐mode stationary phase can be especially beneficial for the development of new drugs which may have specific physical and chemical properties. Data obtained from measurements on three different mixed‐mode columns (WAX‐1, WCX‐1, and HILIC‐1) were used to construct the plots illustrating the relationship between the retention factors of the analytes and organic modifier content, buffer concentration, and buffer pH. As a result of the known chemical structures of the analyzed molecules and analysis of these plots, possible interaction mechanisms in various chromatographic systems were proposed. Conclusions enabled suggestions for the optimization of chromatographic conditions to be made as well as the improved selection of the stationary phase for different types of analytes.
Back Cover: Separation of pharmaceutically active compounds by multimodal chromatography with ultraviolet detection
SEPARATION SCIENCE PLUS
Chemicke Listy, 2002
An HPLC method was developed and validated for rapid determination of amprolium as an undesirable... more An HPLC method was developed and validated for rapid determination of amprolium as an undesirable additive to final fodders. Amprolium is extracted from a sample with a mixture of methanol and dichloromethane and, after purification of the extract on a silica gel column, determined by ion-pair reverse-phase chromatography on C8 with fluorescent detection after postcolumn derivatization with potassium hexacyanoferrate(III) in alkaline medium. The separation of amprolium on the C8 reverse phase and its postcolumn derivatization were optimized. The limit of determination was 86 g.kg-1, the repeatability 0.1 mg/kg and the yield of the method was 102 5.5 % at amprolium concentrations 0.5 - 5 mg/kg.. The repeatability was determined on real samples of final fodders.
Opdmalizace melody HPLC pro stanovení amprolia v krmivech pro obsahy menší neŽ 5 mg.kg-1 s postkolonovou derivatizací
Chemicke Listy, 2002
An HPLC method was developed and validated for rapid determination of amprolium as an undesirable... more An HPLC method was developed and validated for rapid determination of amprolium as an undesirable additive to final fodders. Amprolium is extracted from a sample with a mixture of methanol and dichloromethane and, after purification of the extract on a silica gel column, determined by ion-pair reverse-phase chromatography on C8 with fluorescent detection after postcolumn derivatization with potassium hexacyanoferrate (III) in alkaline medium. The separation of amprolium on the C8 reverse phase and its postcolumn derivatization were optimized. The limit of determination was 86 μg.kg - 1 , the repeatability 0.1 mg.kg - 1 and the yield of the method was 102′5.5 % at amprolium concentrations 0.5-5 mg.kg - 1 . The repeatability was determined on real samples of final fodders.
Chemicke Listy, Aug 15, 2002
Determination of Ionophoric Polyether Monocarboxylic Acids in Feedstuffs by HPLC with Post-Column Derivatization
Chemicke Listy, 2005
A fast HPLC method for determination of low contents of monensin, salinomycin and narasin in feed... more A fast HPLC method for determination of low contents of monensin, salinomycin and narasin in feedstuff was developed and validated. The ionophores were extracted from samples with a hexane - ethyl acetate mixture and, after purification on a Sep-Pak Silica column, they were determined by HPLC on C18 reverse phase using post-column derivatization with 4-(dimethylamino)benzaldehyde and UV detection at 598 nm. The preseparation, separation and derivatization reaction of the ionophores were optimized. New derivatization reagents (salicylaldehyde, thiophene-2-carbaldehyde, 4-methoxybenzaldehyde, 4-hydroxy-3,5-dimethoxybenzaldehyde and ethylvanilin) were tested. For monensin, salinomycin and narasin, the respective parameters were as follows: determination limit 7.5, 266 and 503 μg.kg-1; repeatability 0.08 and 0.06 mg.kg-1 (content 0.2-5 mg.kg-1); recovery 99.0 ± 8.4, 97.0 ± 6.0 and 99.2 ± 5.1 % (content 1-5 mg.kg-1)
Nitrites as precursors of N-nitrosation in pharmaceutical samples – A trace level analysis
Journal of Pharmaceutical and Biomedical Analysis, 2022
Determination of methylbenzoquate in premixes and animal feeds using liquid chromatography with fluorescence detection
Journal of AOAC International, 2005
A rapid analytical procedure was developed and tested for routine identification and quantificati... more A rapid analytical procedure was developed and tested for routine identification and quantification of methylbenzoquate in feeds by liquid chromatography (LC). The ground feed samples were extracted using methanol-water (80 + 20, v/v) at 65 degrees-70 degrees C in a water bath for premixes and in dichloromethane at 45 degrees C in a water bath for final feeds, respectively. The extract of final feeds was cleaned using solid-phase extraction on silica columns. Both the final feed and premix extracts were analyzed by reversed-phase LC on a NovaPak C18 column (3.9 x 150 mm; 4 microm) with methanol-acetonitrile-water-phosphoric acid (340 + 350 + 308 + 2, v/v) as mobile phase. Fluorescence detection was performed at excitation and emission wavelengths of 265 and 390 nm, respectively. Alternatively, post-column addition of sulfuric acid solution was used to decrease the determination limit. The recovery of methylbenzoquate, in a concentration range of 0.5-10 mg/kg, was 105.0 +/- 7.3%. The...
Chemicke Listy, 2007
Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological a... more Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological activity of α-tocopherol. At present, eight such derivatives are included in the vitamin E family: α-,?? β-,γ- and δ-tocopherol and α-,β-,γ- and δ-tocotrienol. The vitamin E content in food and feeds is expresed as that of α-tocopherol. The aim of this paper was to monitor the content of tocopherols and tocotrienols in food and feed materials and their mixtures. The contents were recalculated as α-tocopherol equivalents (α-TE). The α-toco¬pherol contents and α-TEs were compared. The content of the other tocopherols and tocotrienols in food and compounded feeds does not significantly contribute to the α-TEs.
Rapid determination of amoxicillin in premixes by HPLC
Journal of Pharmaceutical and Biomedical Analysis, 2005
A rapid analytical procedure for routine identification and quantification of amoxicillin in prem... more A rapid analytical procedure for routine identification and quantification of amoxicillin in premixes by high performance liquid chromatography was developed and tested. The ground premix samples were extracted for 10 min using 100ml extraction mixture water-methanol (800:200, v/v). The extract was analyzed by reversed-phase on Agilent Zorbax SB-C18 column (4.6 mm x 150 mm, i.d., 5 microm particle size) with water-methanol-phosphoric acid-triethylamine (842:150:4:4) containing 10 mM hexane-1-sulfonic acid sodium salt (pH 3.5) as mobile phase. UV detection was carried out at 230 nm. The method was validated for specificity, linearity, solution stability, accuracy, precision, limit of detection, and limit of determination. The detector response for amoxicillin was linear over the selected concentration range from 2.0 to 40.0 mg ml(-1) with a correlation coefficient 0.9999. The mean accuracy was 100.1% with a standard deviation of 0.6%. The limit of detection and the limit of determination are 0.1 and 0.3 mg ml(-1), respectively, which corresponds to 10 and 30 mg kg(-1), respectively, in real premix sample. The sample and standard solutions were stable for 4 h. The method is selective and can be used in routine analysis.
Liquid chromatographic separation of pregabalin and its possible impurities with fluorescence detection after postcolumn derivatization with o-phtaldialdehyde
Journal of Pharmaceutical and Biomedical Analysis, 2010
A rapid procedure based on direct extraction and RP-HPLC separation of pregabalin and its possibl... more A rapid procedure based on direct extraction and RP-HPLC separation of pregabalin and its possible impurities with fluorescence detection has been developed. The separation conditions and parameters of derivatization reaction for postcolumn derivatization of pregabalin with o-phtaldialdehyde/2-mercaptoethanol were studied. Purospher STAR RP-8e column with isocratic elution was employed. Fluorescence detection was performed at excitation and emission wavelength of 345 nm and 450 nm, respectively. The proposed method has an advantage of a simple sample pre-treatment and a quick and very sensitive HPLC method. The applicability of developed method was successfully verified during analysis of commercial samples of tablets of Lyrica (Pfizer, USA).
Journal of Pharmaceutical and Biomedical Analysis, 2011
Different pharmaceutical preparations against the common cold containing phenylephrine (PHE) and ... more Different pharmaceutical preparations against the common cold containing phenylephrine (PHE) and saccharose were studied. New impurities were discovered in these preparations after exposure using isocratic ion-pair chromatography separation on a C18 column. LC-MS and NMR techniques were employed to identify and to fully characterize these new compounds. The products were identified as 1-[5-(hydroxymethyl)-2-furyl]-2-methyl-1,2,3,4-tetrahydroisochinolin-4,8-diol and 1-[5-(hydroxymethyl)-2-furyl]-2-methyl-1,2,3,4-tetrahydroisochinolin-4,6-diol. Identification of these degradation products allowed to understand and to confirm their formation mechanism. The developed HPLC method separates of all known impurities and impurities originated from PHE as well.
Journal of Pharmaceutical and Biomedical Analysis, 2014
Potential causes for the formation of synthetic impurities that are present in solithromycin (1) ... more Potential causes for the formation of synthetic impurities that are present in solithromycin (1) during the laboratory development are studied in the article. These impurities were monitored by HPLC, and their structures are identified on the basis of MS and NMR spectroscopy. In addition to the synthesis, characterization of these seven impurities, strategies for minimizing them to the level accepted by ICH are also described.
Journal of AOAC INTERNATIONAL, 2012
A rapid HPLC method for the analytical resolution of cinacalcet enantiomers was developed. Four c... more A rapid HPLC method for the analytical resolution of cinacalcet enantiomers was developed. Four chiral columns (two amylose and two cellulose type) were evaluated in RP systems. Excellent enantioseparation with a resolution of more than 6 was achieved on Chiralpak AY (amylose 5-chloro-2-methylphenylcarbamate chiral stationary phase) using 10 mM triethylamine (pH 8.0)–acetonitrile (40 + 60, v/v) mobile phase. Validation of the HPLC method, including linearity, LOD, LOQ, precision, accuracy, and selectivity, was performed according to the International Conference on Harmonization guidelines. The method was successfully applied for the determination of (S)-cinacalcet in enantiopure active pharmaceutical ingredient (R)-cinacalcet.
Journal of Pharmaceutical and Biomedical Analysis, 2012
A new impurity was detected and determined using gradient ion-pair UHPLC method with UV detection... more A new impurity was detected and determined using gradient ion-pair UHPLC method with UV detection in zolmitriptan (ZOL). Using MS, NMR and IR study the impurity was identified as (4S,4 S)-4,4-(2,2-(4-(dimethylamino)butane-1,1-diyl)bis(3-(2-(dimethylamino) ethyl)-1H-indole-5,2diyl))bis(methylene)di(oxazolidin-2-one) (ZOL-dimer). The standard of ZOL-dimer was consequently prepared via organic synthesis followed by semipreparative HPLC purification. The UHPLC method was optimized in order to selectively detect and quantify other known and unknown process-related impurities and degradation products of ZOL as well. The presented method which was validated with respect to linearity, accuracy, precision and selectivity has an advantage of a very quick UHPLC chromatographic separation (less than 7 min including re-equilibration time) and therefore is highly suitable for routine analysis of related substances and stability studies of ZOL.
Chemicke Listy, 2007
Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological a... more Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological activity of α-tocopherol. At present, eight such derivatives are included in the vitamin E family: α-,β-,γ- and 8-tocopherol and α-,β-,γ- and δ-tocotrienol. The vitamin E content in food and feeds is expresed as that of α-tocopherol. The aim of this paper was to monitor the content of tocopherols and tocotrienols in food and feed materials and their mixtures. The contents were recalculated as α-tocopherol equivalents (a-TE). The α-tocopherol contents and α-TEs were compared. The content of the other tocopherols and tocotrienols in food and compounded feeds does not significantly contribute to the α-TEs.
The determination of two analogues of 4-(azidomethyl)-1,1'-biphenyl as potential genotoxic impurities in the active pharmaceutical ingredient of several sartans containing a tetrazole group
Journal of Pharmaceutical and Biomedical Analysis
Supercritical fluid chromatography in chiral separations: Evaluation of equivalency of polysaccharide stationary phases
Journal of Separation Science
Nine different chiral columns based on covalently immobilized or coated tris(3,5-dimethylphenylca... more Nine different chiral columns based on covalently immobilized or coated tris(3,5-dimethylphenylcarbamate) cellulose and amylose have been explored. We evaluated their respective enantioselective potential including the quality of enantioseparation and qualitative characteristics of peaks. The generic screening conditions were using gradient elution from 5% to 40% organic modifier/CO2 during 3 min with about forty enantiomer pairs. Primary screening was carried out using ten different mobile phases varying in type of additives while using one representative amylose- and one cellulose-based column. The complete evaluation of all nine columns was then carried out using three best performing organic modifiers: (i) methanol + 0.1% trifluoroacetic acid + 0.1% diethylamine, (ii) isopropanol + 0.1% trifluoroacetic acid + 0.1% diethylamine, and (iii) methanol + 0.1% ammonium hydroxide. Equivalency of different columns with the same chiral selector was not confirmed. When comparing coated stationary phases, the similarity corresponded to 62 % and 63 %, for cellulose-based and 67 % and amylose-based columns. For immobilized columns the similarity was 69 % and 59 % for celluloses and amyloses, respectively. The best performing column based on success rate of enantioseparation was Chiralcel OD-3 when using methanol + 0.1% trifluoroacetic acid and 0.1% diethylamine combined additive. This article is protected by copyright. All rights reserved.
Chiral separation of aliphatic primary amino alcohols as o -phthaldialdehyde/mercaptoethanol derivatives on polysaccharide-based chiral stationary phases
Chirality
A sensitive chiral high performance liquid chromatography (HPLC) method for the determination of ... more A sensitive chiral high performance liquid chromatography (HPLC) method for the determination of aliphatic primary amino alcohol isomers with o-phthaldialdehyde/mercaptoethanol precolumn derivatization has been developed and validated. Seven chiral columns were tested in a reversed phase mode. Excellent enantioseparation with the resolution more than 2.0 was achieved on Chiralcel OJ-3R. The effect of various chromatographic conditions including column temperature, acetonitrile content in the mobile phase, buffer pH, buffer concentration, and buffer type in the mobile phase on the retention and the selectivity was investigated. The final mobile phase consisted of binary mixture of 20mM ammonium formate solution with acetonitrile (75:25; v/v). The analyses were performed at mobile phase flow rate of 1.0 mL/min and the column temperature of 40°C. The fluorescence detection was performed at excitation wavelength of 345 nm and emission wavelength of 450 nm. The developed method was fully validated in terms of linearity, sensitivity, accuracy, precision, intermediate precision, and selectivity according to International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines using internal normalization procedure. The proposed chiral method was proved to be highly sensitive, simple, and rapid and was successfully applied to the determination of D-Valinol content in commercially available samples of L-Valinol.
Journal of chromatographic science, Jan 13, 2017
Unknown impurities were identified in ibuprofen (IBU) soft gelatin capsules (SGCs) during long-te... more Unknown impurities were identified in ibuprofen (IBU) soft gelatin capsules (SGCs) during long-term stability testing by a UHPLC method with UV detection and its chemical formula was determined using high resolution/accurate mass (HRAM) LC-MS. Reference standards of the impurities were subsequently synthesized, isolated by semi-preparative HPLC and characterized using HRAM LC-MS, NMR and IR. Two impurities were formed by esterification of IBU with polyethylene glycol (PEG), which is used as a fill of the SGCs, and were identified as IBU-PEG monoester and IBU-PEG diester. Two other degradants arised from reaction of IBU with sorbitol and sorbitan, which are components of the shell and serves as plasticizers. Thus, IBU sorbitol monoester (IBU-sorbitol) and IBU sorbitan monoester (IBU-sorbitan ester) were identified. An UHPLC method was further optimized in order to separate, selectively detect and quantify the degradation products in IBU SGCs.
Separation of pharmaceutically active compounds by multimodal chromatography with ultraviolet detection
Separation science plus, Jun 18, 2021
This research focused on pharmaceutically active ingredients analyzed by mixed‐mode liquid chroma... more This research focused on pharmaceutically active ingredients analyzed by mixed‐mode liquid chromatography. For this purpose, 16 analytes were chosen with acidic, basic, or neutral properties that were analyzed under different conditions. These analytes play an important role in the pharmaceutical industry and improved separation will make drug control more efficient. Mixed‐mode chromatography is becoming an increasingly popular method for the analysis of diverse compounds due to the process being based on the combination of two or more interaction modes. The use of the mixed‐mode stationary phase can be especially beneficial for the development of new drugs which may have specific physical and chemical properties. Data obtained from measurements on three different mixed‐mode columns (WAX‐1, WCX‐1, and HILIC‐1) were used to construct the plots illustrating the relationship between the retention factors of the analytes and organic modifier content, buffer concentration, and buffer pH. As a result of the known chemical structures of the analyzed molecules and analysis of these plots, possible interaction mechanisms in various chromatographic systems were proposed. Conclusions enabled suggestions for the optimization of chromatographic conditions to be made as well as the improved selection of the stationary phase for different types of analytes.
Back Cover: Separation of pharmaceutically active compounds by multimodal chromatography with ultraviolet detection
SEPARATION SCIENCE PLUS
Chemicke Listy, 2002
An HPLC method was developed and validated for rapid determination of amprolium as an undesirable... more An HPLC method was developed and validated for rapid determination of amprolium as an undesirable additive to final fodders. Amprolium is extracted from a sample with a mixture of methanol and dichloromethane and, after purification of the extract on a silica gel column, determined by ion-pair reverse-phase chromatography on C8 with fluorescent detection after postcolumn derivatization with potassium hexacyanoferrate(III) in alkaline medium. The separation of amprolium on the C8 reverse phase and its postcolumn derivatization were optimized. The limit of determination was 86 g.kg-1, the repeatability 0.1 mg/kg and the yield of the method was 102 5.5 % at amprolium concentrations 0.5 - 5 mg/kg.. The repeatability was determined on real samples of final fodders.
Opdmalizace melody HPLC pro stanovení amprolia v krmivech pro obsahy menší neŽ 5 mg.kg-1 s postkolonovou derivatizací
Chemicke Listy, 2002
An HPLC method was developed and validated for rapid determination of amprolium as an undesirable... more An HPLC method was developed and validated for rapid determination of amprolium as an undesirable additive to final fodders. Amprolium is extracted from a sample with a mixture of methanol and dichloromethane and, after purification of the extract on a silica gel column, determined by ion-pair reverse-phase chromatography on C8 with fluorescent detection after postcolumn derivatization with potassium hexacyanoferrate (III) in alkaline medium. The separation of amprolium on the C8 reverse phase and its postcolumn derivatization were optimized. The limit of determination was 86 μg.kg - 1 , the repeatability 0.1 mg.kg - 1 and the yield of the method was 102′5.5 % at amprolium concentrations 0.5-5 mg.kg - 1 . The repeatability was determined on real samples of final fodders.
Chemicke Listy, Aug 15, 2002
Determination of Ionophoric Polyether Monocarboxylic Acids in Feedstuffs by HPLC with Post-Column Derivatization
Chemicke Listy, 2005
A fast HPLC method for determination of low contents of monensin, salinomycin and narasin in feed... more A fast HPLC method for determination of low contents of monensin, salinomycin and narasin in feedstuff was developed and validated. The ionophores were extracted from samples with a hexane - ethyl acetate mixture and, after purification on a Sep-Pak Silica column, they were determined by HPLC on C18 reverse phase using post-column derivatization with 4-(dimethylamino)benzaldehyde and UV detection at 598 nm. The preseparation, separation and derivatization reaction of the ionophores were optimized. New derivatization reagents (salicylaldehyde, thiophene-2-carbaldehyde, 4-methoxybenzaldehyde, 4-hydroxy-3,5-dimethoxybenzaldehyde and ethylvanilin) were tested. For monensin, salinomycin and narasin, the respective parameters were as follows: determination limit 7.5, 266 and 503 μg.kg-1; repeatability 0.08 and 0.06 mg.kg-1 (content 0.2-5 mg.kg-1); recovery 99.0 ± 8.4, 97.0 ± 6.0 and 99.2 ± 5.1 % (content 1-5 mg.kg-1)
Nitrites as precursors of N-nitrosation in pharmaceutical samples – A trace level analysis
Journal of Pharmaceutical and Biomedical Analysis, 2022
Determination of methylbenzoquate in premixes and animal feeds using liquid chromatography with fluorescence detection
Journal of AOAC International, 2005
A rapid analytical procedure was developed and tested for routine identification and quantificati... more A rapid analytical procedure was developed and tested for routine identification and quantification of methylbenzoquate in feeds by liquid chromatography (LC). The ground feed samples were extracted using methanol-water (80 + 20, v/v) at 65 degrees-70 degrees C in a water bath for premixes and in dichloromethane at 45 degrees C in a water bath for final feeds, respectively. The extract of final feeds was cleaned using solid-phase extraction on silica columns. Both the final feed and premix extracts were analyzed by reversed-phase LC on a NovaPak C18 column (3.9 x 150 mm; 4 microm) with methanol-acetonitrile-water-phosphoric acid (340 + 350 + 308 + 2, v/v) as mobile phase. Fluorescence detection was performed at excitation and emission wavelengths of 265 and 390 nm, respectively. Alternatively, post-column addition of sulfuric acid solution was used to decrease the determination limit. The recovery of methylbenzoquate, in a concentration range of 0.5-10 mg/kg, was 105.0 +/- 7.3%. The...
Chemicke Listy, 2007
Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological a... more Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological activity of α-tocopherol. At present, eight such derivatives are included in the vitamin E family: α-,?? β-,γ- and δ-tocopherol and α-,β-,γ- and δ-tocotrienol. The vitamin E content in food and feeds is expresed as that of α-tocopherol. The aim of this paper was to monitor the content of tocopherols and tocotrienols in food and feed materials and their mixtures. The contents were recalculated as α-tocopherol equivalents (α-TE). The α-toco¬pherol contents and α-TEs were compared. The content of the other tocopherols and tocotrienols in food and compounded feeds does not significantly contribute to the α-TEs.
Rapid determination of amoxicillin in premixes by HPLC
Journal of Pharmaceutical and Biomedical Analysis, 2005
A rapid analytical procedure for routine identification and quantification of amoxicillin in prem... more A rapid analytical procedure for routine identification and quantification of amoxicillin in premixes by high performance liquid chromatography was developed and tested. The ground premix samples were extracted for 10 min using 100ml extraction mixture water-methanol (800:200, v/v). The extract was analyzed by reversed-phase on Agilent Zorbax SB-C18 column (4.6 mm x 150 mm, i.d., 5 microm particle size) with water-methanol-phosphoric acid-triethylamine (842:150:4:4) containing 10 mM hexane-1-sulfonic acid sodium salt (pH 3.5) as mobile phase. UV detection was carried out at 230 nm. The method was validated for specificity, linearity, solution stability, accuracy, precision, limit of detection, and limit of determination. The detector response for amoxicillin was linear over the selected concentration range from 2.0 to 40.0 mg ml(-1) with a correlation coefficient 0.9999. The mean accuracy was 100.1% with a standard deviation of 0.6%. The limit of detection and the limit of determination are 0.1 and 0.3 mg ml(-1), respectively, which corresponds to 10 and 30 mg kg(-1), respectively, in real premix sample. The sample and standard solutions were stable for 4 h. The method is selective and can be used in routine analysis.
Liquid chromatographic separation of pregabalin and its possible impurities with fluorescence detection after postcolumn derivatization with o-phtaldialdehyde
Journal of Pharmaceutical and Biomedical Analysis, 2010
A rapid procedure based on direct extraction and RP-HPLC separation of pregabalin and its possibl... more A rapid procedure based on direct extraction and RP-HPLC separation of pregabalin and its possible impurities with fluorescence detection has been developed. The separation conditions and parameters of derivatization reaction for postcolumn derivatization of pregabalin with o-phtaldialdehyde/2-mercaptoethanol were studied. Purospher STAR RP-8e column with isocratic elution was employed. Fluorescence detection was performed at excitation and emission wavelength of 345 nm and 450 nm, respectively. The proposed method has an advantage of a simple sample pre-treatment and a quick and very sensitive HPLC method. The applicability of developed method was successfully verified during analysis of commercial samples of tablets of Lyrica (Pfizer, USA).
Journal of Pharmaceutical and Biomedical Analysis, 2011
Different pharmaceutical preparations against the common cold containing phenylephrine (PHE) and ... more Different pharmaceutical preparations against the common cold containing phenylephrine (PHE) and saccharose were studied. New impurities were discovered in these preparations after exposure using isocratic ion-pair chromatography separation on a C18 column. LC-MS and NMR techniques were employed to identify and to fully characterize these new compounds. The products were identified as 1-[5-(hydroxymethyl)-2-furyl]-2-methyl-1,2,3,4-tetrahydroisochinolin-4,8-diol and 1-[5-(hydroxymethyl)-2-furyl]-2-methyl-1,2,3,4-tetrahydroisochinolin-4,6-diol. Identification of these degradation products allowed to understand and to confirm their formation mechanism. The developed HPLC method separates of all known impurities and impurities originated from PHE as well.
Journal of Pharmaceutical and Biomedical Analysis, 2014
Potential causes for the formation of synthetic impurities that are present in solithromycin (1) ... more Potential causes for the formation of synthetic impurities that are present in solithromycin (1) during the laboratory development are studied in the article. These impurities were monitored by HPLC, and their structures are identified on the basis of MS and NMR spectroscopy. In addition to the synthesis, characterization of these seven impurities, strategies for minimizing them to the level accepted by ICH are also described.
Journal of AOAC INTERNATIONAL, 2012
A rapid HPLC method for the analytical resolution of cinacalcet enantiomers was developed. Four c... more A rapid HPLC method for the analytical resolution of cinacalcet enantiomers was developed. Four chiral columns (two amylose and two cellulose type) were evaluated in RP systems. Excellent enantioseparation with a resolution of more than 6 was achieved on Chiralpak AY (amylose 5-chloro-2-methylphenylcarbamate chiral stationary phase) using 10 mM triethylamine (pH 8.0)–acetonitrile (40 + 60, v/v) mobile phase. Validation of the HPLC method, including linearity, LOD, LOQ, precision, accuracy, and selectivity, was performed according to the International Conference on Harmonization guidelines. The method was successfully applied for the determination of (S)-cinacalcet in enantiopure active pharmaceutical ingredient (R)-cinacalcet.
Journal of Pharmaceutical and Biomedical Analysis, 2012
A new impurity was detected and determined using gradient ion-pair UHPLC method with UV detection... more A new impurity was detected and determined using gradient ion-pair UHPLC method with UV detection in zolmitriptan (ZOL). Using MS, NMR and IR study the impurity was identified as (4S,4 S)-4,4-(2,2-(4-(dimethylamino)butane-1,1-diyl)bis(3-(2-(dimethylamino) ethyl)-1H-indole-5,2diyl))bis(methylene)di(oxazolidin-2-one) (ZOL-dimer). The standard of ZOL-dimer was consequently prepared via organic synthesis followed by semipreparative HPLC purification. The UHPLC method was optimized in order to selectively detect and quantify other known and unknown process-related impurities and degradation products of ZOL as well. The presented method which was validated with respect to linearity, accuracy, precision and selectivity has an advantage of a very quick UHPLC chromatographic separation (less than 7 min including re-equilibration time) and therefore is highly suitable for routine analysis of related substances and stability studies of ZOL.
Chemicke Listy, 2007
Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological a... more Vitamin E is a collective term for fat-soluble chroman-6-ol derivatives that exhibit biological activity of α-tocopherol. At present, eight such derivatives are included in the vitamin E family: α-,β-,γ- and 8-tocopherol and α-,β-,γ- and δ-tocotrienol. The vitamin E content in food and feeds is expresed as that of α-tocopherol. The aim of this paper was to monitor the content of tocopherols and tocotrienols in food and feed materials and their mixtures. The contents were recalculated as α-tocopherol equivalents (a-TE). The α-tocopherol contents and α-TEs were compared. The content of the other tocopherols and tocotrienols in food and compounded feeds does not significantly contribute to the α-TEs.
The determination of two analogues of 4-(azidomethyl)-1,1'-biphenyl as potential genotoxic impurities in the active pharmaceutical ingredient of several sartans containing a tetrazole group
Journal of Pharmaceutical and Biomedical Analysis
Supercritical fluid chromatography in chiral separations: Evaluation of equivalency of polysaccharide stationary phases
Journal of Separation Science
Nine different chiral columns based on covalently immobilized or coated tris(3,5-dimethylphenylca... more Nine different chiral columns based on covalently immobilized or coated tris(3,5-dimethylphenylcarbamate) cellulose and amylose have been explored. We evaluated their respective enantioselective potential including the quality of enantioseparation and qualitative characteristics of peaks. The generic screening conditions were using gradient elution from 5% to 40% organic modifier/CO2 during 3 min with about forty enantiomer pairs. Primary screening was carried out using ten different mobile phases varying in type of additives while using one representative amylose- and one cellulose-based column. The complete evaluation of all nine columns was then carried out using three best performing organic modifiers: (i) methanol + 0.1% trifluoroacetic acid + 0.1% diethylamine, (ii) isopropanol + 0.1% trifluoroacetic acid + 0.1% diethylamine, and (iii) methanol + 0.1% ammonium hydroxide. Equivalency of different columns with the same chiral selector was not confirmed. When comparing coated stationary phases, the similarity corresponded to 62 % and 63 %, for cellulose-based and 67 % and amylose-based columns. For immobilized columns the similarity was 69 % and 59 % for celluloses and amyloses, respectively. The best performing column based on success rate of enantioseparation was Chiralcel OD-3 when using methanol + 0.1% trifluoroacetic acid and 0.1% diethylamine combined additive. This article is protected by copyright. All rights reserved.
Chiral separation of aliphatic primary amino alcohols as o -phthaldialdehyde/mercaptoethanol derivatives on polysaccharide-based chiral stationary phases
Chirality
A sensitive chiral high performance liquid chromatography (HPLC) method for the determination of ... more A sensitive chiral high performance liquid chromatography (HPLC) method for the determination of aliphatic primary amino alcohol isomers with o-phthaldialdehyde/mercaptoethanol precolumn derivatization has been developed and validated. Seven chiral columns were tested in a reversed phase mode. Excellent enantioseparation with the resolution more than 2.0 was achieved on Chiralcel OJ-3R. The effect of various chromatographic conditions including column temperature, acetonitrile content in the mobile phase, buffer pH, buffer concentration, and buffer type in the mobile phase on the retention and the selectivity was investigated. The final mobile phase consisted of binary mixture of 20mM ammonium formate solution with acetonitrile (75:25; v/v). The analyses were performed at mobile phase flow rate of 1.0 mL/min and the column temperature of 40°C. The fluorescence detection was performed at excitation wavelength of 345 nm and emission wavelength of 450 nm. The developed method was fully validated in terms of linearity, sensitivity, accuracy, precision, intermediate precision, and selectivity according to International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines using internal normalization procedure. The proposed chiral method was proved to be highly sensitive, simple, and rapid and was successfully applied to the determination of D-Valinol content in commercially available samples of L-Valinol.
Journal of chromatographic science, Jan 13, 2017
Unknown impurities were identified in ibuprofen (IBU) soft gelatin capsules (SGCs) during long-te... more Unknown impurities were identified in ibuprofen (IBU) soft gelatin capsules (SGCs) during long-term stability testing by a UHPLC method with UV detection and its chemical formula was determined using high resolution/accurate mass (HRAM) LC-MS. Reference standards of the impurities were subsequently synthesized, isolated by semi-preparative HPLC and characterized using HRAM LC-MS, NMR and IR. Two impurities were formed by esterification of IBU with polyethylene glycol (PEG), which is used as a fill of the SGCs, and were identified as IBU-PEG monoester and IBU-PEG diester. Two other degradants arised from reaction of IBU with sorbitol and sorbitan, which are components of the shell and serves as plasticizers. Thus, IBU sorbitol monoester (IBU-sorbitol) and IBU sorbitan monoester (IBU-sorbitan ester) were identified. An UHPLC method was further optimized in order to separate, selectively detect and quantify the degradation products in IBU SGCs.